Development of Radial Polarity in Arabidopsis Embryogenesis Lateral organs of the plant shoot (cotyledons, leaves, floral organs) are polarized along their proximal-distal, medial-lateral and adaxial-abaxial axes. Recent analysis of mutations that affect adaxial-abaxial polarity in lateral organs suggests that adaxial-abaxial polarity is fundamentally related to the central-peripheral (radial) polarity of the shoot itself. Vascular tissue is a fundamental feature of shoot radial pattern, and it is known that the plant hormone auxin plays an important role in vascular differentiation. Furthermore, mutations in several auxin-related genes display embryonic defects. Adaxial-abaxial and central-peripheral polarity is established during embryogenesis by an unknown mechanism(s). By examining the expression of molecular markers of radial polarity in mutants that affect auxin transport, perception, signaling or response, I will test the hypothesis that auxin plays an important role in the establishment of radial polarity in the embryo. In addition, I will use a novel marker of peripheral/abaxial identity in a genetic screen to identify genes that are required for specification of radial polarity in the embryo. Together, these studies should provide insight into the generation of radial pattern in embryogenesis.